Re: DataSets vs Serviced Component - C# Discussion Boards

4-Aug-03 22:14

Hello,

I'm experiencing a problem with DataSets. If I use a DataSet as a parameter of a method in a Serviced Component, I always receive an InvalidCastException because something is trying to convert __ComObject to DataSet. When a method only returns a DataSet (no DataSet as parameter) there's no problem.

I'm running my application with framework 1.1, the serviced component is in Server mode.

Is this some bug in the .Net framework? Confused | :confused:

Has anyone a solution or a workaround for this problem?

best regards,
Pieter

Ista5-Aug-03 9:34

5-Aug-03 9:34

I don't know the answer but does the dataset serialize. You might have to implement the serializable interface. or just shoot it as an xml stream through. Com passes it as a stream anyhow.

I'm not an expert yet, but I play one at work. Yeah and here too.

schockp5-Aug-03 21:06

5-Aug-03 21:06

Thanks for replying. I'm not sure if a dataset is serializable, I'll check it out.

Running the component in Library mode doesn't have this problem, although there's a problem with my database connection. But that's some security issue I think.

Ista6-Aug-03 4:26

6-Aug-03 4:26

it might be easier to parse it as xml "WriteXML() method" then send it through

I'm not an expert yet, but I play one at work. Yeah and here too.

schockp6-Aug-03 4:32

6-Aug-03 4:32

I think that the dataset-to-xml and xml-to-dataset coversion will cause a significant performance drop.

Jarrod Marshall6-Aug-03 7:40

Jarrod Marshall

6-Aug-03 7:40

I ran into this problem working with C# based queued components.
Datasets are serializable, they support ISerializable however alot of things with COM+ (especially with Queued Components) is that they need the components to support IPersist.

They have no idea how to serialize using the ISerializable interface therefore you either go the route of dataset--> XML, XML--> dataset or implement IPersist within your component.

schockp6-Aug-03 20:46

6-Aug-03 20:46

Jarrod,

Thanks, I'll take a look at how to implement the IPersist interface.

Pieter

Ista6-Aug-03 10:26

6-Aug-03 10:26

Well its relatively fast and uses a buffered stream. I mean really when your marshalling your Dataset you serialize the object to text then back again. And its basically the same thing. WriteXML is the fastest firehose method of the class. But yeah it would be better to do a dataset. You might try createing an object, clone the dataset to that object then marshalling it over the boundary. That might work. Or use the serializable attribute above a custom class that inherits the dataset.

Personally, With DataSets I use reflection to populate classes then update them with COM+ life cycles. Much more elegant and easier to load balance. That and business rules on forms and behind the scenes are simple to implement.

nick

I'm not an expert yet, but I play one at work. Yeah and here too.

schockp6-Aug-03 20:45

6-Aug-03 20:45

Nick,

Thanks for your input! I'm really new to Serviced Components and COM+. Can you explain your way of working a bit more? I don't understand what you mean with:

Ista wrote:
With DataSets I use reflection to populate classes then update them with COM+ life cycles

Yeah, I know what reflection is, but the combination with datasets and populate classes is unclear to me.

Pieter

Ista7-Aug-03 6:21

diff. threads access gui resource

7-Aug-03 6:21

Well simply put I create a class

LastName

FirstName

SSN

if table looks like

EmployeeID
LastName
FirstName
SocialSecurityNumber

then my select would look like:

SELECT EmployeeID = ID, LastName, FirstName, SSN = SocialSecurityNumber

then I would use a DataReader becuase its much faster

For each row I would create the class based on the primaryID ( EmployeeID )

Then I would iterate through the GetValues array returned by the datareader

using reflection I use the PropertyType and propertyInfo classes to populate the fields. I haven't taken on the method part but thats next month on my development cycle

nick

I'm not an expert yet, but I play one at work. Yeah and here too.

zecodela4-Aug-03 21:19

zecodela

4-Aug-03 21:19

hi,
i used the serial port class in msdn to do serial communication in C#.
in the receiver thread, i try to send notice message to richtext box create in another thread. sometimes, i will got NullReferenceException. it come mainly i switch windows or do other time consumption task in windows.
i think it related to using diff. thread to access GUI resource.
do you think so? and, any method to do inter-threading commu. in C#? just raise some keywords for me to search is enough.
thanks,
jim

Re: diff. threads access gui resource

Furty4-Aug-03 21:53

Furty

4-Aug-03 21:53

zecodela wrote:
i think it related to using diff. thread to access GUI resource

You think correctly - you must only access form controls from the originating thread. Here's the keyword thast will solve all your problems: Invoke

There's a couple of articles here on CP that deal with multi-threading issues in Windows Forms - both are useful, especially the one by James T Johnson, look them up.

ListView drag drop example?

azusakt4-Aug-03 15:41

azusakt

4-Aug-03 15:41

Dear members,
I'm making a listview that allows user to drag (row)items to different index recently. However, I can't find a good example for doing that.
Does anyone knows how to use drag-drop event on ListView? Or anyone knows where has good example?

In my ListView, suppose each item has 6 subitems, when I drag an item (e.g.) index 5 to index 1, then all data of item 5 are inserted into row 1.
I know this is not hard, and many of our members knows that. Please teach me

Please help me..... Thanks a lot~

I've tried to make the code, but it looks a bit strange.

e.g. I have items 1,2,3,....10.
if I selected 2,4,5,6 and drag to the position of item 3. Suppose, item 2,4,5,6 will move under item3 .. like 1,3,2,4,5,6...

but how can I prevent some selected items not to do anything if I move to there position? e.g. 4,5,6,7 are selected, if I move to 5 or 6, the program won't do anything.

Could you help me to see how to implement this code? Or do you know what is the best way to do this?

Here is the codes inside my listview drag drop function:

<br />
if(OList.SelectedItems.Count==0)<br />
return;<br />
Point cp = OList.PointToClient(new Point(e.X, e.Y));<br />
ListViewItem ToItem = OList.GetItemAt(cp.X, cp.Y); <br />
<br />
if(ToItem==null)<br />
return;<br />
<br />
int num = ODS_List.SelectedItems.Count;<br />
int locationIndex = ToItem.Index-1;<br />
for(int i=0; i { <br />
ListViewItem dragItem = OList.SelectedItems[i];<br />
if(locationIndex!=dragItem.Index) <br />
return;<br />
<br />
ListViewItem insertItem = (ListViewItem)dragItem.Clone();<br />
OList.Items.Insert(locationIndex, insertItem);<br />
locationIndex++;<br />
}<br />
<br />
foreach(ListViewItem olditem in OList.SelectedItems)<br />
{<br />
OList.Items.Remove(olditem); <br />
}<br />

Thank you very very much.

Re: ListView drag drop example?

Khang Nguyen5-Aug-03 12:17

Khang Nguyen

5-Aug-03 12:17

Hi,

Do a search for something like "ListView" and "Drag Drop" from this forum, there is a chance that you will find some examples. Here is one:

http://www.codeproject.com/cs/miscctrl/dragdroplistviewreorder1.asp?target=listview%7Cdrag%7Cdrop

Hope you get more tips
Khang
Big Grin | :-D

Datagrid CurrentCellChanged problem

work_to_live4-Aug-03 14:07

work_to_live

4-Aug-03 14:07

I have an ArrayList bound to a datagrid. I've developed a method of validating the data entered in the TextBoxes, and forcing the user to re-enter invalid data. Unfortunately, I use the CurrentCellChanged event to test if it's necessary to move the selection back to the cell with the invalid data in it. It works fine with one exception. If you're at the end of a row of data, and press the TAB key (return is fine), you get an extra CurrentCellChanged event. The first one takes you to the beginning of the same row, and the next one takes you to the next row! This messes with my logic that determines if it's necessary to move the selection back to the cell with the error in it.

Is there some way to inhibit the handling of the TAB key once you've determined that you want to select another cell?

Re: Datagrid CurrentCellChanged problem

Ista8-Aug-03 19:25

8-Aug-03 19:25

Yeah but you gotta override the PreviewKeyMessage function. Also you need to creat a custom table style

I'm not an expert yet, but I play one at work. Yeah and here too.

oledbcommand

K4reem4-Aug-03 13:14

K4reem

4-Aug-03 13:14

i want to make an oledbCommand with a variable as in sql @variable..SELECT *Table From Table WHERE Column=(thatvariable),how can i declare this to use in my code, am using Microsoft Access

Ista4-Aug-03 17:58

4-Aug-03 17:58

OleDbConnection oleConn = new OleDbConnection(<myconnectionstring>);
oleCOnn.Open();

OleDbDataAdpater oleAdapter = new OleDbDataAdapter("my select statemnent", oleConn);

DataSet ds = new DataSet("Access");

oleAdapter.Fill(ds, "MyTable");

now I would check the parameters because its been 2 weeks since I connected but it should work fine

ohh yeah to test

DataGrid1.DataSource = ds.Tables["MyTable"];

I'm not an expert yet, but I play one at work. Yeah and here too.

K4reem5-Aug-03 3:53

K4reem

5-Aug-03 3:53

thx Ista for replying Rose | [Rose]

, but that wasnt my question i was just asking about how to declare an oledb parameter as in SELECT *Table From Table WHERE Column=(parameter),as declared in sql we use "@" b4 the parameter i was just asking wat i ll declare in ole instead of that "@". Confused | :confused:

Ista5-Aug-03 9:33

5-Aug-03 9:33

doh

its just like the sql

myOleCommand.Parameters.Add("@Param1", OleDbType.SmallInt);

refer to it as

myOleCommand.Parameters["@Param1"].Value = 1;

i use a short way when assigning many

OleDbParameterCollection olePar = myOldCommand.Parameters;
olePar.Parameters.Add("@Param2", OleDbType.VarChar, 10);
olePar["@Param2"].Value = "Hey dude";

I think that answers it. Sorry for the confusion.

nick

I'm not an expert yet, but I play one at work. Yeah and here too.

K4reem5-Aug-03 9:51

K4reem

5-Aug-03 9:51

thx Ista really for replying again Rose | [Rose]

but i still ve the problem!
this is my debug error :
@PostionIndex error: managed EE does not understand expression's syntax

the code :
OleDbCommand cmd = new OleDbCommand("SELECT * FROM Phones WHERE Contact = @PostionIndex");
cmd.Parameters.Add("@PostionIndex", OleDbType.SmallInt);
cmd.Parameters["@PostionIndex"].Value = int.Parse(this.editID.Text);
Confused | :confused:

Ista5-Aug-03 9:57